1. Field of the Invention
This invention relates to a change speed apparatus for a working vehicle that engages in an operation while moving forward and backward. The change speed apparatus is constructed to produce a high forward speed stage for changing a speed of torque received from an input shaft to a high forward speed and transmitting it to an output shaft, a low forward speed stage for changing the speed of torque received from the input shaft to a low forward speed and transmitting it to the output shaft, a backward speed stage for changing the speed of torque received from the input shaft to a low backward speed and transmitting it to the output shaft, and a neutral stage.
2. Description of the Related Art
This type of change speed apparatus is disclosed in Japanese Patent Publication (Unexamined) H11-78574, for example. This apparatus has an auxiliary gear change speed mechanism that produces a low forward speed stage and a backward speed stage, which is incorporated into a main gear change speed mechanism that produces four, a first to a fourth, speeds. The main gear change speed mechanism is shiftable by a first shift lever, while the auxiliary gear change speed mechanism is shiftable by a second shift lever. With the second shift lever placed in a low forward speed position, a high forward speed position or a backward position, the first shift lever is appropriately operable to set a total of four speeds, i.e. the first speed, second speed, third speed and fourth speed. Consequently, eight forward speeds and four backward speeds in total may be produced. In this change speed apparatus, however, components of the main gear change speed mechanism and auxiliary gear change speed mechanism are arranged together in a complicated manner. Thus, the change speed apparatus has a complex construction, with a disadvantage of assembling difficulties.
Regarding control positions of the second shift lever which is the shift lever of the auxiliary gear change speed mechanism, as shown in FIG. 13A, a low forward speed position L is disposed to one side (vehicle's forward moving side) of a neutral region N extending transversely, and a high forward speed position H and a reverse position R are arranged to the other side (vehicle's backward moving side) of the neutral region N. A mirror image of this arrangement is shown in FIG. 13B. Such an arrangement of control positions provides good operability, with a linear shift control path linking the low forward speed position L and reverse position R, allowing a switching between low forward speed movement and backward movement, which is required frequently during an operation, to be carried out only by moving the shift lever linearly. However, though low forward speed position L is disposed to the vehicle's forward moving side with respect to the neutral region N, the high forward speed position H is disposed to the side opposite from the low forward speed position L (vehicle's backward moving side) with respect to the neutral region N. This causes an inconvenience that, for a fast forward movement, the shift lever has to be moved in the opposite direction (i.e. vehicle's backward moving direction) to a slow forward movement.